Amyloids are misfolded proteins that are structurally similar to and include prions.' Amyloids are implicated in the pathogeneis of more than 40 different diseases including the common neurodegenerative disorders Alzheimer's and Parkinson's diseases. The long-term goals of this project include characterization of the pathways leading to amyloid formation and disease pathology, in order to guide the development of improved therapeutic and diagnostic approaches to the prion diseases and other amyloidoses. In the infectious amyloidoses caused by prions, the prion protein (PrP) folds into aberrant conformation denoted PrPSc. The infectious prion particle is comprised solely of PrPSc molecules in mammals. Prion diseases include Creutzfeldt-Jakob disease (CJD) and related hereditary disorders as well as the infectious human maladies variant CJD and kuru. The animal prion diseases include bovine spongiform encephalopathy ("mad cow disease"), scrapie in sheep and chronic wasting disease in deer. Our studies using X-ray fiber diffraction and a variety of complementary techniques are aimed at determining the molecular structures of several different amyloids. The first group of amyloids comprise peptides derived from non-infectious amyloids. These are more tractable for structural analysis, and will serve as models for prion structure. These polypeptides include those associated with Alzheimer's, Huntington's, and several other diseases. The second group is composed of amyloidogenic peptides derived from prions; these include a 55-residue fragment of the prion protein harboring the PrP mutation P102L that causes Gerstmann-Straussler- Scheinker disease. The third group includes the purified N-terminally truncated and full-length PrPSc that are infectious. These will be isolated from scrapie-infected mouse and hamster brains. Structure determination will require the construction of molecular models, and the development and refinement of these models using data from X-ray fiber difraction. Electron microscopy will provide low-resolution constraints on molecular models; where available, published partial structure information from X-ray crystallography or solid state NMR will be incorporated. Published models, which are generally in marked disagreement with each other, will be evaluated.